1. Field of the Invention
The present invention relates to an ink jet printer head having orifices for discharging an ink jet to effect recording, and also relates to a manufacturing method for such an ink jet printer head. More particularly, the present invention relates to an on-demand type ink jet printer head and a manufacturing method therefor.
2. Description of Related Art
An ink jet printer head having orifices for discharging an ink jet and depositing the same onto a printing paper to effect recording is now in practical applications as a kind of printer heads capable of effecting quick and high-density printing.
In an on-demand type ink jet printer head, a pair of body plates are bonded together, and a plurality of recesses are formed on a bonding surface of one of the body plates to define a plurality of pressure chambers. Further, a plurality of displaceable pressure applying surfaces of a pressure generating section are exposed to the pressure chambers. In such an ink jet printer head, the pressure applying surfaces of the pressure generating section are selectively vibrated by applying a driving voltage according to print image information, and an ink contained in the pressure chambers corresponding to the pressure applying surfaces thus vibrated is pressurized to be discharged as an ink jet from a plurality of orifices communicating with the pressure chambers.
FIG. 23 shows an ink jet printer head as disclosed in Japanese Patent Laid-open No. Hei 3-73348 as an example of the related art. As shown in FIG. 23, an ink jet printer head 1 is generally constructed of a pair of body plates, i.e., a channel plate 2 and a driver plate 3 bonded together. A plurality of recesses 4 are formed on a bonding surface of the channel plate 2, and a plurality of projections 5 as driving portions are formed so as to project a base 3a of the driver plate 3 so that end surfaces 9 of the projections 5 are respectively exposed to the recesses 4. A space 6 defined between the adjacent projections 5 is filled with an elastic material 7. Thus, a bonding surface of the driver plate 3 is formed as a flat surface. The flat bonding surface of the driver plate 3 is bonded to the bonding surface of the channel plate 2 to close the recesses 4, thereby defining a plurality of pressure chambers 8. The end surfaces 9 of the projections 5 exposed to the pressure chambers 8 serve as pressure applying surfaces for applying pressure to ink (not shown) contained in the pressure chambers 8. A driving power source 11 is connected to the pressure applying surfaces 9 and base portions 10 of the projections 5. Although not shown, an orifice plate is actually bonded to a front surface of an assembly of the plates 2 and 3.
In the ink jet printer head 1 mentioned above, the projections 5 of the driver plate 3 are selectively expanded and contracted by a driving voltage from the driving power source 11. Accordingly, the pressure applying surfaces 9 of the projections 5 are displaced to apply a pressure to the ink contained in the pressure chambers 8 of the channel plate 2, thereby discharging the ink as an ink jet from orifices of the orifice plate. To pressurize the ink in the pressure chambers 8 with high efficiency, the width of each projection 5 is set to be smaller than that of each pressure chamber 8, and the elastic material 7 is filled between the adjacent projections 5.
Further, it has been proposed that a piezoelectric ceramic is used as the material of the pressure generating section of such an ink jet printer head. As piezoelectric ceramic has a good corrosion resistance and strength, it can be utilized as a structural material for forming the pressure chambers. In this regard, it has been demanded to improve the productivity and increase the density of arrangement of the pressure chambers in forming the pressure chambers by utilizing piezoelectric ceramic.
For example, in an ink jet printer head as disclosed in Japanese Patent Laid-open No. Sho 55-17575, a comb-like pressure generating section having a plurality of driving portions arrayed in spaced relationship from each other is formed by selectively etching a surface of a piezoelectric ceramic plate, and another pressure generating section having similar driving portions is also formed by selectively etching a surface of another piezoelectric ceramic plate. Then, end surfaces of the driving portions of both the pressure generating sections are bonded together to thereby define each pressure chamber by the adjacent driving portions of both the pressure generating sections. Similarly, in an ink jet printer head as disclosed in Japanese Patent Laid-open Nos. Sho 62-56150, Sho 63-129173 and Hei 2-150355, a comb-like pressure generating section having a plurality of driving portions arrayed in spaced relationship from each other is formed by cutting (e.g., dicing) one surface or both surfaces of a piezoelectric ceramic plate, and a flat cover plate is bonded to end surfaces of the driving portions of the pressure generating section, thereby defining each pressure chamber by the adjacent driving portions of the pressure generating section.
Further, in an ink jet printer head as disclosed in Japanese Patent Laid-open Nos. Sho 60-90770 and Hei 3-10845, a comb-like pressure generating section having a plurality of driving portions arrayed in spaced relationship from each other is formed by cutting or the like of a piezoelectric ceramic plate, and an elastic vibration plate is sandwiched between the pressure generating section and a channel plate having a plurality of recesses so that end surfaces of the driving portions are respectively opposed through the vibration plate to the recesses, thereby defining each pressure chamber by each recess.
However, as each of the pressure generating sections as disclosed in each of the above cited references is formed from a piezoelectric ceramic plate, the formation of the driving portions is difficult and cracks are apt to form at the driving portions.
To solve this problem, the present assignee has proposed an improved manufacturing method for an ink jet printer head in Japanese Patent Application No. Hei 3-161172 wherein a pressure generating section having a plurality of driving portions is formed by injection molding of piezoelectric ceramic. According to this method, the pressure generating section formed of piezoelectric ceramic can be uniformly mass-produced to thereby improve the productivity.
Now, the problems in the above-mentioned related art will be described. First, in the ink jet printer head 1 as disclosed in Japanese Patent Laid-open No. Hei 3-73348, each space 6 between the adjacent projections 5 of the driver plate 3 is filled with the elastic material 7 to thereby attain high-efficiency pressurization of the ink contained in the pressure chambers 8. However, considering the demand of high-density arrangement of the orifices and the pressure chambers 8 to improve print quality, the driving portions 5 of the driver plate 3 must be very finely formed, so that it is difficult to fill the elastic material 7 in each narrow space 6 between the adjacent projections 5 arranged with a high density. Furthermore, in bonding the channel plate 2 and the driver plate 3 to each other, it is necessary to precisely position the fine recesses 4 and the fine projections 5, causing a further reduction in productivity.
On the other hand, according to the manufacturing method for the ink jet printer head in Japanese Patent Application No. Hei 3-161172 proposed by the present assignee, the pressure generating section can be easily mass-produced by injection molding of piezoelectric ceramic. Further, the present assignee has also proposed that the pressure generating section may be formed by extrusion molding of piezoelectric ceramic, so that the pressure generating section can also be easily mass-produced by extrusion molding of piezoelectric ceramic. However, as the pressure generating section is formed as an integral body by injection molding or extrusion molding, the driving portions are integrally formed with a plate-like base portion. Accordingly, when a driving voltage is applied to the driving portions of the pressure generating section, an electric field acts also to the base portion, causing deformation of the base portion. As a result, there is a possibility that the operational characteristics of the driving portions will be hindered by generating cross talk or the like. As measures for reducing the cross talk, it has purposed to thin the base portion. In this case, however, the pressure generating section is apt to be broken in injection molding or extrusion molding of piezoelectric ceramic, causing a reduction in productivity. Further, the plate-like base portion is apt to be curved in baking a molded body obtained by injection molding or extrusion molding, causing a reduction in yield.
In bonding a pair of plates constituting an ink jet printer head as mentioned above, ultrasonic bonding is desirably adopted because any portion other than the bonding surfaces of the plates is not heated and the required time for bonding is short, thus contributing to the improvement in productivity. In the case of ultrasonic bonding, fine projections called edges are formed on the bonding surfaces in general, and these edges are molten to effect the bonding of the two plates. In this case, however, the formation of the edges reduces the productivity. Accordingly, ultrasonic bonding is sometimes carried out without forming the edges. The present inventors actually prepared a pair of plates having no edges to examine the bonding performance of ultrasonic bonding without forming the edges. As a result, it was found that narrow portions of the bonding surfaces were well bonded together but wide portions of the bonding surfaces were hard to bond. Further, it was also found that the continuation of ultrasonic bonding till the completion of bonding of the wide portions caused excessive melting of the narrow portions.